1. Field of the Invention
The present invention relates to a wireless communication system. And, more particularly, the present invention relates to a method for transmitting control information in wireless communication system and apparatus therefor.
2. Discussion of the Related Art
In a mobile communication system, a user equipment may receive information from a base station via downlink, and the user equipment may also transmit information via uplink. The information received or transmitted by the user equipment includes data and diverse control information. And, various physical channels may exist depending upon the type and purpose of the information received or transmitted by the user equipment.
FIG. 1 illustrates physical channels that are used in a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system, which is an example of a mobile communication system and a general signal transmitting method using the same.
When a power of a user equipment is turned off and then turned back on, or when a user equipment newly enters (or accesses) a cell, the user equipment performs an initial cell search process, such as synchronizing itself with the base station in step S101. For this, the user equipment may receive a P-SCH (Primary Synchronization Channel) and an S-SCH (Secondary Synchronization Channel) from the base station so as to be in synchronization with the base station, and the user equipment may also acquire information, such as cell ID. Thereafter, the user equipment may receive a Physical Broadcast Channel so as to acquire broadcast information within the cell. Meanwhile, the user equipment may receive Downlink Reference Signal (DL RS), in the step of initial cell search, so as to verify the downlink channel status.
The user equipment that has completed the initial cell search may receive a Physical Downlink Control Channel (PDCCH) and a Physical Downlink Shared Channel (PDSCH) based upon the Physical Downlink Control Channel (PDCCH) information, in step S102, so as to acquire more detailed system information.
Meanwhile, the user equipment that has not yet completed the initial cell search may perform a Random Access Procedure, such as in steps S103 and S106 of a later process, so as to complete the access to the base station. In order to do so, the user equipment transmits a characteristic sequence through a Physical Random Access Channel (PRACH) as a preamble (S103), and then the user equipment may receive a response message respective to the random access through the PDCCH and its respective PDSCH (S104). In case of a contention based random access, excluding the case of a handover, the user equipment may perform Contention Resolution Procedures, such as transmitting an additional Physical Random Access Channel (PRACH) (S105) and receiving a Physical Downlink Control Channel (PDCCH) and a Physical Downlink Shared Channel (PDSCH) corresponding to the PDCCH.
After performing the above-described procedures, the user equipment may receive a Physical Downlink Control Channel (PDCCH)/Physical Downlink Shared Channel (PDSCH) (S107), as a general uplink/downlink signal transmission procedure, and may then perform Physical Uplink Shared Channel (PUSCH)/Physical Uplink Control Channel (PUCCH) transmission (S108).
FIG. 2 illustrates a signal processing procedure performed by the user equipment for transmitting uplink signals.
In order to transmit an uplink signal, a scrambling module 210 of the user equipment may scramble a transmission signal by using a user equipment specific scrambling signal. Then, the scrambled signal is inputted to a modulation mapper 220 so as to be modulated to a complex symbol by using a Binary Phase Shift Keying (BPSK) scheme, a Quadrature Phase Shift Keying (QPSK) scheme, or a 16 Quadrature Amplitude Modulation (16QAM) scheme, based upon a type of the transmission signal and/or a channel status. Afterwards, the modulated complex symbol is processed by a conversion precoder 230 and then inputted to a resource element mapper 240. Herein, the resource element mapper 240 may map the complex symbol to a time-frequency resource element, which is to be used in the actual transmission. The processed signal may then pass through an SC-FDMA signal generator 250 so as to be transmitted to the base station through an antenna.
FIG. 3 illustrates a signal processing procedure performed by the base station for transmitting downlink signals.
In a 3GPP LTE system, a base station may transmit one or more code words. Accordingly, each of the one or more code words may be processed as a complex symbol by a scrambling module 301 and a modulation mapper 302, just as described in the uplink of FIG. 2. Subsequently, each of the complex symbols may be mapped to a plurality of layers by a layer mapper 303, and each layer may be multiplied by a predetermined precoding matrix, which is selected based upon the channel status, by a precoding module 304, thereby being allocated to each transmission antenna. Each of the processed transmission signals respective to an antenna is mapped to a time-frequency resource element, which is to be used in the actual transmission, by a respective resource element mapper 305. Thereafter, each of the transmission processed signals passes through an Orthogonal Frequency Division Multiple Access (OFDM) signal generator 306 so as to be transmitted through each antenna.
In a mobile communication system, when the user equipment transmits a signal via uplink, a Peak-to-Average Ratio (PAPR) may be more disadvantageous then when the base station performs transmission via downlink. Therefore, as described above in association to FIG. 2 and FIG. 3, unlike the OFDMA scheme, which is used in downlink signal transmission, the Single Carrier-Frequency Division Multiple Access (SC-FDMA) scheme is used in uplink signal transmissions.
FIG. 4 illustrates an SC-FDMA scheme for transmitting uplink signals and an OFDMA scheme for transmitting downlink signals in a mobile communication system.
Herein, a user equipment for uplink signal transmission and a base station for downlink signal transmission are identical to one another in that each of the user equipment and the base station includes a Serial-to-Parallel Converter 401, a subcarrier mapper 403, an M-point IDFT module 404, and a Cyclic Prefix (CP) adding module 406.
However, the user equipment for transmitting signals by using the SC-FDMA scheme additionally includes a Parallel-to-Serial Converter 405 and an N-point IDFT module 402. And, herein, the N-point IDFT module 402 is configured to cancel a predetermined portion of an IDFT processing influence caused by the M-point IDFT module, so that the transmission signal can have a single carrier property. FIG. 5 illustrates a frequency-domain signal mapping method for satisfying a single carrier characteristic within the frequency domain. In FIG. 5, (a) represents a localized mapping method, and (b) represents a distributed mapping method. The localized mapping method is defined in the current 3GPP LTE system.
Meanwhile, description will now be made on a clustered SC-FDMA, which corresponds to a corrected form of the SC-FDMA. In sequentially performing a subcarrier mapping process between the DFT process and the IFFT process, the clustered SC-FDMA divides DFT process output samples into sub-groups, so that an IFFT sample input unit can map each sub-group to subcarrier regions, which are spaced apart from one another. And, in some cases, clustered SC-FDMA may include a filtering process and a cyclic extension process.
At this point, a sub-group may be referred to as a cluster, and cyclic extension refers to a process of inserting a guard interval, which is longer than a maximum delay spread of a channel, between consecutive (or contiguous) symbols in order to prevent inter-symbol interference (ISI) while each subcarrier symbol is being transmitted through a multi-path channel.